Escalating Thirst

Endangered Western Tree Habitats

A team of scientists at the University of Grenoble, in France, have isolated ultrasonic pops 100 times faster than what a human can hear in slivers of dead pine wood bathed in a hydrogel to simulate the conditions of a living tree. They exposed the gel to an artificially dry environment and listened for the noises that occurred as air bubbles built up, blocking water uptake, similar to what occurs to trees during drought. As leaves on a tree collect carbon dioxide, they open their pores, a process that leaves them particularly vulnerable to water loss.

Douglas firs and pine trees can repair this damage as frequently as every hour, says Katherine McCulloh, a plant ecophysiologist at Oregon State University. However, the bubbles are deadly for other species.

Today, the typical forest in the often thirsty American West contains an unnaturally high density of 112 to 172 trees per acre. Besides intercepting rain and snow that would otherwise enter the groundwater supply, such an overabundance threatens native species. “Deprived of [the effect of] low-intensity, naturally occurring fires, aspen, lupine, sequoia and fireweed can’t reproduce,” notes Jamie Workman, of the Environmental Defense Fund. “Deer lose edge habitat. Threatened owls and raptors can’t navigate through increasingly dense thickets.” Workman argues that thinning out small trees is the answer.

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Scientists are warning that if humans don’t reduce greenhouse gas emissions drastically and maintain natural carbon sinks like forests within 10 years, the impact on Earth’s climate will be catastrophic.